Installing Android SDK requires manually downloading all required packages. This task becomes painful if you want to have it on multiple machines, requiring you repeat the download procedure on each work station. APD(Android Offline SDK Installer) saves this overhead by allowing you to install Android SDK in offline mode. APD offers downloading packages from web to enable offline installation or select already downloaded packages for offline installation on your machine. You can download APD here.
Android SDK is available for free. Whether you want to develop applications or games, Android SDK provides you access to Application Programming Interface (API) of Android Platform. Coupled with Eclipse IDE, Android SDK is powerful tool which allows you to develop and debug your applications on emulator. Android SDK comes with every release of Android OS, providing updated APIs, emulator configurations and sample projects. You can download Android SDK from Android Developer website